The invention relates to a method for treating and, especially, for the cleaning, abrasive stripping or clearing of coatings, graffiti or other superficial contamination on parts, workpieces or surfaces made of stone, concrete, wood, metal, plastic, glass, ceramic or paper, whereby a blasting agent is gravity fed from a supply container to a carrying air stream which is guided inside a hose system consisting of incoming and outgoing lines, transported by means of negative pressure through the same and blasted from a blasting chamber through a blasting lance against the surface to be treated, and from there transported back into the carrying air stream, so that the blasting agent in recirculated.
The invention relates also to a device for implementing the method with a supply container with a conically shaped lower end as a discharge funnel provided with an outlet opening for feeding a fine-grained and/or coarse-grained blasting agent, which by gravity reaches the outlet opening of the discharge funnel, which via a flexible incoming line for the transport of the blasting agent is connected with a blasting chamber, which can be evacuated by means of an underpressure-producing aggregate and accommodate the parts and surfaces, which in turn is connected with an outgoing underpressure line, whereby through an opening in the blasting chamber a blast lance connected with the incoming underpressure line provided with a nozzle is guided.
The invention relates also to the use of sodium hydrogen carbonate, thermoset plastic particles, ash, comminuted fine-grained slag, corundum, quartz, metallic particles, glass beads, vegetable/organic particles or mixtures thereof for the removal of paint, spray paint, graffiti or other contaminants.
It is known to remove coatings or other contaminants such an deposits from walls with a blasting treatment with grains blasting agents which are blasted with an overpressure of 10 to 300 bar against the object to be blasted. The blasting agent, mostly fine-grained sand or metal particles, is transported to the blasting location with a copressed air stream (see DE 31 27 012 A1, DE 34 13 576 A1, DE 37 38 246 A1, DE 40 03 324 A1, DE 40 14 085 C1, DE 41 43 113 C; DE 42 01 860 C1).
From DE-OS 29 16 131 a surface is treated with the aid of a container provided at its lower end with a discharge funnel with an outlet for a grinding agent, with a pistol guiding the grinding agent unto the surface to be treated. The pistol is traversed by a channel at whose end a compressed-air source is connected. An incoming line connects the outlet of the container with the channel in the pistol at a point upstream of the connection with the compressed-air source. An opening is provided in the incoming line close to the outlet, through which the atmospheric pressure is in communication with the incoming line, so that the compressed air which flows through the pistol channel and over the end of the incoming line generates a negative pressure in the incoming line which sucks air through the opening, whereby the grinding agent is aspirated through the outlet and blasted against the surface to be treated at the other end of the pistol channel.
The barrel of the pistol is surrounded by a hood, which can be positioned on the surface to be treated. From the hood a return line leads to the container, on which also a vacuum source is connected, which generates a negative pressure over the stored grinding agent, which aspirates from the hood the materials blasted against the surface to be treated.
With this known system two circuits are established, a negative pressure circuit for the aspiration of the used blasting material and an overpressure circuit which accelerates the blasting material to the necessary blasting velocity, whereby the addition of the blasting material in the overpressure circuit is performed with the negative pressure created by the overpressure. Both circuits are separated from each other by the blasting material stored in the container acting as a pressure barrier.
Finally for the production of the necessary blasting velocity, this known system also works with an overpressure which must be delivered to the blasting pistol and is energy consuming. The additionally required negative pressure generator in the collection container complicates matters even more.
Due in part to the considerable overpressure the blasting agents have a high impact energy, which in the case of a sensitive substrate, for instance plastic surfaces, can lead to damage or even destruction. A gentle detachment without damage to the substrate is not possible.
A further disadvantage in that a separation of the detached lacquer layer from the blasting material does not take place, i.e. the contaminated blasting material has to be discarded and replaced.
From the DE-OS 44 07 956 a sand blasting box is known for the surface treatment of preferably flat material surfaces, which on its frontal side has an opening whereinto the frontal end of a sand blasting pistol connected to a compressed-air source is introduced. The rear side of the sand blasting box has a treatment window with an elastic sealing strip, which can be positioned over the material surface to be treated. The blasting sand is directed by means of compressed air, i.e. under overpressure, onto the surface to be treated. A commercially available household vacuum cleaner in connected to the sand blasting box. which produces a negative pressure in the blasting box and aspirates the blasting material. The barrel of the blasting pistol is guided in the blasting box by means of a rubber diaphragm arranged at the end and is capable of swinging motion in order to project the blasting material at various angles and distances onto the treatment surface.
Also in this known solution the blasting material receives its blasting and moving energy through overpressure. Again two separate circuits are required, namely an overpressure circuit in the form of a compressed-air stream for the transport of the sand to the pistol and a negative pressure circuit for the aspiration of the sand exiting the pistol. Therefore the costs are high.
After blasting the blasting material is contaminated with the removed matter. There is no separation, so that also in this system the blasting material has to be discarded or separately processed again. The stream of blasting material created by the overpressure is extremely energy-rich and not suited for the detachment of coating from problematic soft substrates, because it in not possible to adjust the blasting energy.
The DE 36 29 623 A1 discloses a device for cleaning of surfaces of large objects with a granular blasting agent, with a blasting basket movable parallel to the object surface, wherein over an open side a blast against the surface of the object can be created and which captures and evacuates the particles of blasting material with the detached dirt particles ricocheting from the material surface. This apparatus is connected with an operator cabin equipped with observation windows, so that the installation is in plain view of the operator and forms a mobile work unit together with the cabin. The blasting space is connected via a flexible line with a negative pressure space, wherein separating devices for the separation of the exhaust air, recyclable blasting agents and residuals are provided. The recycled blasting agent is guided towards a spinner, whose rotational velocity sets the blasting intensity.
A recirculation of the blasting agent is achieved, but here too a circuit for the aspiration of used blasting agent through negative pressure and a circuit for the actuation of a blasting turbine with a spinner are required. The blasting agent receive its energy through the rotation of the spinner, which in expensive from the point of view of equipment and control technology. For the removal of for instance graffiti such a construction is much too complicated and consumes too much energy.
DE 196 14 555 A1 describes a device and a method for the abrasive blasting, particularly sand blasting, of workpieces, especially smaller workpieces, for instance in the hobby field.
The device described in this reference consists of a chamber substantially airtight on all sides with at least one, preferably more closable openings, whereby the chamber can be evacuated, a container for receiving the blasting agent, a blasting pipe unit, which can be introduced into the chamber through one of the displaceable openings and which has an inlet for the blasting agent and an inlet for air and an outlet opening for the blasting agent, whereby the inlet for the blasting agent can be connected with the blast agent container via an incoming line. The blasting pipe unit has a pipe-like main part with an inlet for the blasting agent, an air inlet opening and an outlet opening, respectively nozzle for the blasting agent and the aspired air. After the introduction of the blasting pipe unit through one of the chamber openings, the air inlet opening is outside the chamber and the air outlet opening is inside the chamber. By means of a commercially available vacuum cleaner connected to the chamber atmospheric air is aspirated through the air inlet opening, due to the negative pressure in the chamber the blasting agent in transported from the container through the incoming line and through the outlet opening of the blasting pipe unit in the chamber it is guided onto the work piece to be treated. With the vacuum cleaner the air and the blasting agent are aspirated from the chamber and caught in the filter of the vacuum cleaner.
The apparatus described in DE 196 14 555 A1 has the drawback that the achieved blasting velocities are sufficient only for the cleaning of small workpieces. This solution is not suited for large workpieces or surfaces. Besides the blasting process can be performed only as long as the supply of blasting agent in the container lasts.
The blasting material contaminated with dirt is merely disposed of in the vacuum cleaner. A separation of the blasting material from the contamination does not take place, just as there is no return of the blasting material to the blasting circuit.
This proposed solution is not suited for a large-surface blasting treatment, such as for instance surfaces defaced by graffiti spraying, The same applies to larger parts or workpieces.
It in the object of the invention to improve a method and a device of the kind mentioned in the introduction, so that coatings, paint, dirt and deposits on parts or on flat or curved open and/or closed surfaces can be removed without overpressure and high pressure generators, energetically, gently and free of dust, with no or with insignificant detriment to the substrate, with low energy consumption, high flexibility and environmentally safe recovery and recycling of the blasting agent.
According to the invention this object in achieved in that the acceleration of the blasting agent is essentially produced by the negative pressure applied to the blasting chamber and by increasing the blasting velocity in an acceleration section by means of diameter reductions from the incoming line to the acceleration section.
In a preferred embodiment of the method of the invention, the negative pressure in circulation is set at 50 to 300 mbar, the blasting agent is added by gravity and/or underpressure in an amount of 0.01 to 25% by volume of the carrying air stream, with or without cleaning fluid, the blasting-agent/air mixture is rectilinearly accelerated without deflection to a blasting velocity of 20 to 80 m/s prior to its impact on the treatment surface. After that, the blast agent and air are directed onto the treatment surface with a rhythmically repeated back and forth motion over the treatment surface under surveillance, or the treatment surface is set to rotate and/or to swing in the blasting-agent/air mixture. The blasting-agent/air mixture together with the detached dust, dirt or the removed matter is aspirated due to the produced underpressure and set into rotation in such a way that the blasting agent in separated due to its higher mans from the blasting-agent/air mixture. The particles of the blasting agent are collected, optionally dried and again fed into the volume of carrying air stream due to gravity and/or underpressure, and the remaining dust/air mixture is subjected to a fine cleaning in the wet and/or dry extractor, and fresh air and/or optionally the separated air are then again. fed into the circuit, cooled or heated.
In a further preferred feature the acceleration of the blasting agent takes place in the rectilinear acceleration section inside the incoming underpressure line, prior to its entering the blasting lance.
According to a further preferred embodiment, at a constant volume flow the blasting agent is additionally accelerated due to a diameter reduction in the incoming line down to 0.1 to 0.9 times of its diameter (d1) over a length of equalling 5 to 50 times the inner diameter (d2) of the diameter-reduced incoming line.
Therefore the velocity of the blasting agent can be correspondingly increased prior to its entering the blasting lance, and the specific impact energy of the blasting particles can be extremely sensitively adjusted by altering the diameter ratio d2:d1, the length of the acceleration section and the distance of the frontal end of the blasting lance from the treatment surface.
With the method of the invention it becomes therefore possible to adjust the kinetic energy of the blasting particles to the type, size and configuration of the coating and the substrate.
Blasting agent such as sodium hydrogen carbonate, plastic particles, preferably duroplastic particles, ashes, comminuted fine-grained slag, corundum, quartz, metallic particles, glass beads, vegetable/organic particles or mixtures thereof are particularly well suited for an adjustment of the blasting velocity through diameter reduction.
Depending on the kind of blasting particles and the imparted blasting velocity, with the method of the invention it is possible to abrasively remove coatings from metal, spray paint from plastic, inscriptions on paper, weathering deposits on stone, dirt deposits on concrete, if necessary without the abrasion of the substrate, or with substrate abrasion also to remove rust layers from metals. The abrasiveness of the method of the invention depends in a decisive measure on the blasting energy transmitted to the blasting particles and on their type.
The method of the invention is characterized in that the blasting energy can be varied in accordance with the nature of the substrate, the characteristics of the blasting agent and the kind of the coating to be removed, so that also problematic grime, such as for instance repeated coats of paint, can also be detached from the substrate, without destroying the substrate or causing any significant damage.
The treatment effect of the blasting particles in further improved according to the invention, when the blasting agent is wetted prior to its acceleration with conventional cleaning fluids.
Primarily in the case of graffiti defacing of larger surfaces a blasting chamber is sealingly and displaceably positioned on the substrate to be treated, evacuated and the blasting-agent/air mixture is moved back and forth over the treatment surface.
The back and forth motion acts an a pendulum and/or swinging motion of the blasting-agent/air mixture in the blasting chamber within a limited angle range within a cone with an opening angle of 30xc2x0 to 120xc2x0, preferably 90xc2x0.
The sliding motion of the blasting chamber from one treatment surface to another is preferably performed under the applied negative pressure. Naturally it is also possible to perform the displacement of the blasting chamber under atmospheric pressure with a short circuit, without leaving the framework of the invention.
In cases where the workpieces have to be treated for deposits or rust according to the method of the invention, the workpieces are in addition set to rotate or swing in the blasting-agent/air mixture. This can be done stationarily or also by displacing the blasting chamber.
After the blasting agent has hit the respective treatment surface, it is discharged from the blasting chamber due to the applied underpressure, separated from the air stream, optionally cleaned and returned to the circuit. The carrying air can escape into the environment or, according to a special feature of the invention, it is returned to the underpressure circulation after being either heated or cooled, to the extent that the treating of the treatment surface requires a specific temperature. This enhances considerably the efficiency of the treatment.
A particular advantage of the implementation of the method of the invention is that commercially available units can be used without alteration. Depending on the required air output, they are laid out in a single or in multiple steps.
Particularly good treatment results are obtained in the removal of for instance thin paint layers from sheet metal surfaces when to the volume flow of the air carrier 0.013% blasting agent is added.
The object of the invention is further achieved by means of a device with the following features:
a) the incoming underpressure line in connected to an accelerating tube forming a rectilinear acceleration section, which is arranged upstream of the blasting lance and which has a reduced diameter with respect to the incoming line;
b) the incoming underpressure line connected to the outlet opening of the container discharge funnel is provided with a dosage device and/or an injector for the dosage of the blasting agent in circulation;
c) the outgoing underpressure line is connected with at least one further container arranged on the container discharge funnel, which in turn has a conical discharge funnel and is connected with the aggregate producing the negative pressure, whereby the outgoing underpressure line engages tangentially through the container shell into a separator; and
d) upstream in the incoming underpressure line a wetting device is integrated, which can be coupled and uncoupled for the wetting of the blasting agent with cleaning fluid.
In a further preferred embodiment of the device of the invention, the acceleration tube extends over a length which is 5 to 50 times the inner diameter d1 of the incoming underpressure line, whereby the acceleration tube has an inner diameter d2, which is 0.1 to 0.9 times the inner diameter d1 of the incoming underpressure line.
According to yet another preferred embodiment, the acceleration tube can also be directly connected to the dosage device and/or the injector. There should be a rectilinear acceleration section of sufficient length allowing the blasting agent to assume the required blasting velocity.
The length of the acceleration section can be variable, in that an extensible telescopic tube can form the acceleration tube.
In a further embodiment of the invention, the blasting lance reaching into the blasting chamber in pivotable within a cone of approximately 90xc2x0 inside the blasting chamber and is adjustable to various blasting distances. Furthermore the pivotability of the blasting lance is made visible from the outside due to illumination, so that also problem spots can be treated individually.
A further suitable embodiment of the invention provides that the container for the supply of the blasting agent is equipped with an independent ventilation open towards the atmosphere.
The blasting chamber in provided with a funnel which collects the blasting agent ricocheting from the treatment surface and makes sure that the blasting agent reaches the outgoing underpressure line via the suction nozzle.
In a further embodiment of the device of the invention, the blasting chamber consists of a blasting bell open on one side and having a collection funnel, whose open side can be positioned on the treatment surface sealingly under applied underpressure and slidably thereon.
In a further suitable embodiment of the invention, the open side of the blasting bell is associated with a suction plate for sealing a surface to be blasted which in provided with openings.
When for instance a wire mesh has to be cleaned of lacquer and rust coatings, the suction plate is flexible. The suction plate has a covering layer of closed-cell foam rubber. The open side of the blasting bell is positioned on the wire mesh and covered with the suction plate. When underpressure is applied, the covering layer of the suction plate applies itself sealingly to the wire mesh and the bell walls, so that the blasting bell is evacuated. In this way the wire mesh is treated in a simple and advantageous way.
According to a further advantageous embodiment of the device of the invention, the bell walls positioned on the treatment surface are provided with sealing elements which, when underpressure is applied, safely seal off the inner space of the blasting bell against the outer atmospheric pressure.
Preferably the sealing elements consist of closed-call foam rubber, foils, brushes, rubber lips, packed sealing elements, latex hoses, rubber or profile seals which adjust easily to the irregularities of the substrate.
These sealing elements can be detachable from the frontal bell wall, so that in the came of different surface configurations they can easily be exchanged without problems.
In a further feature, the blasting bell applicable to flat treatment surfaces has walls whose and surfaces are even with respect to each other.
For problem areas such an corners, edges or curved treatment surfaces, these walls are convex, concave or V-shaped with respect to each other or provided with articulations which adjust easily to the different surface configurations. This make the use of the device of the inventions particularly effective in corner and edge areas.
A further preferred embodiment of the device of the invention provides a closed blasting chamber, consisting of a stationary or mobile hood and a collection funnel equipped with a suction connection piece applied to the hood, while in the connection plane between hood and funnel a blasting table is arranged.
For the treatment of plastic or metal work pieces, in a preferred feature of this kind of blasting chamber, the blasting table in a rotary plate, whose drive axle is guided into the funnel axle and is connected with a drive fastened to the suction connection piece.
The blasting table can be a swingable plate, which swings about an axis in the connection plane.
With such a rotatable or swingable blasting table special workpieces with a complicated surface structure and shape can be treated quickly and without problems.
To the extent that the type and nature of the surface coating to be detached requires the wetting of the blasting agent with chemicals or cleaning fluids, it is further provided by the invention that a wetting device for the blasting agent be integrated in the incoming underpressure line, downstream of the acceleration section.
In a preferred embodiment of the invention, the acceleration tube and the blasting lance are detachable from each other. This has the advantage that acceleration tubes with various lengths and various inner diameters can be used, so that depending on the type of the substrate, of the coating and of the blasting agent, the required blasting velocity can be set in a dosed manner.
However the acceleration tube and the blasting lance can also be made in one piece. This is connected with the advantage that the blasting lance can be utilized for the length of the acceleration tube, and overall length can be shortened. However then blasting lances with different lengths and different inner diameters have to be made available.
According to a further preferred feature of the device of the invention, the opening of the blasting lance facing the treatment surfaces in provided with a nozzle which can be exchanged.
Depending on the nature of the surface and the type of coating, respectively grime, different nozzle sizes can be affixed to the blasting lance, so that the blasting agent load in the carrying air stream can be correspondingly variable.
The blasting lance is guided through an opening in the blasting bell wall, is sealingly held and swingably supported therein.
According to a preferred embodiment of the invention, this can be done with a ball-and-socket joint arranged in the opening of the blasting chamber wall, as well as with a seal surrounding the opening, flanged to the front wall of the blasting chamber, preferably a shaft seal.
The blasting lance can be equipped with a stop which allows for a change in the blasting distance between the blasting lance opening or the blasting lance nozzle and the treatment surface.
Advantageously the stop is arranged on the blasting lance so that it can slide and be fixed in place, so that the required blasting distance can be precisely set.
It can be suitable to manually guide the blasting lance or turn the workpiece correspondingly.
In a further preferred embodiment of the device of the invention, the blasting chamber is provided with a viewing area, preferably a viewing window, which allows a monitoring of the blasting lance motions and thereby of the blasting process inside the blasting bell. The viewing window is located either above or below the blasting lance. Suitably the viewing window is made of glass or acrylic glass.
Alternately it is also possible to make the entire blasting bell of a transparent impact-resistant plastic material, so that a separate viewing window can be eliminated.
In cases where a stationary blasting chamber is used, the latter has a feeding opening correspondingly sealed against the atmosphere.
Suitable underpressure-producing units are wet and/or dry vacuum devices, pumps, compressors or fans which, according to a further preferred embodiment of the invention, are arranged on the container and are directly connected to the same.
However it is also possible to integrate the unit in the outgoing underpressure line, without leaving the framework of the invention.
Suitably the container for the supply of blasting agent and the container for delivering the blasting agent from the air/dust blasting agent mixture are separated by the discharge funnel of the latter. By means of a slide, valve or a flap, shutter or cellular wheel sluice arranged in the opening of this discharge funnel, this opening in the discharge funnel can be closed, in order to pneumatically separate the two containers from each other.
According to a further advantageous embodiment of the device of the invention, in order to insure that the blasting agent discharged from the carrying air stream is gravity-fed into the supply container and from there reaches the incoming underpressure line without clogging, the discharge funnels in both containers have an opening angle of 30xc2x0 to 120xc2x0, preferably 90xc2x0.
Both containers can have a common housing, which is separated only by the discharge funnel into the outwardly discharging space and the supply space.
According to a further preferred feature in the closed circuit operation of the device of the invention, the outlet connection piece on the underpressure-producing aggregate for the exhaust air is connected with a cooling or heating device and the latter in connected with an incoming underpressure line. Thereby also the temperature can be effective during the treatment, depending on the type and nature of the substrate, the coating and the blasting agent.
With the method and the device of the invention paint, spray paint and graffiti can be effectively removed.
The elimination of the entire overpressure or high-pressure system for the compressed air leads to considerable savings in the energy expenditure.
Besides the method of the invention is very simple to perform, because the blasting process at the treatment surface is monitored. The dosed addition of the blasting agent can be set depending on the coating and the substrate, so that even very thin coatings can be removed without problem, with no damage to the substrate.
This sensitivity of the energy input due to the method of the invention makes it possible to perform restorations on flat or curved surfaces, in addition to the already mentioned applications. Also covers made of plastic, leather or densely impregnated textiles can be treated with the method of the invention.
The device has a compact construction and in user-friendly and extremely flexible due to the use of commercially available components, such as wet-dry vacuum devices.
Due to all these features the solution proposed by the invention meets in an improved way the complex requirements of coating removal from various surfaces with high efficiency, safety, in a maintenance-friendly, controllable and compact manner.